Plastics are suitable for mass production because of easy molding. Moreover, since the plastics possess excellent physical properties such as transparency and impact resistance, they have been widely used as various kinds of packages such as bottle containers, cups, pouches, and packaging sheets.
These packages are packed with various kinds of drinks, seasonings, cosmetics, drugs and the like as contents. However, some of these contents change in quality or deteriorate by a light, and therefore, for the purpose of protecting such contents from the light, the packages are colored in some cases. Furthermore, in order to differentiate commercial products from other similar products by giving the beauties with decorating the packages, the packages are sometimes colored as a part of the decoration of the packages.
In general, the plastic packages are colored by mixing colorant such as pigment or dye into plastic which is main material of the packages. When the coloring agent is mixed, the packages absorb a light having specific wavelength to cause color appearance.
The wavelength of the light absorbed by a substance depends on a chemical structure of the substance, and therefore, in order to obtain a specific color, it is necessary to use a specific chemical substance.
Typical examples of the packages which are colored by mixing the colorant are as follows.
Plastic containers colored green, blue, brown and the like by mixing various pigments or dyes into resins are examples thereof. With these containers, penetration of the wavelength components of the light which is absorbed by coloring components into the containers is restricted, and in consequence, the protection of the contents that are apt to change in quality or to deteriorate owing to a light beam, i.e., visible light barrier performance, is imparted. In addition, the containers colored with a specific color can create a product image and can be differentiated from other products, so that it is possible to enhance buying desire of consumers for the own products.
In recent years, however, from the viewpoints of the saturation of landfill sites and resource saving, the recycle of resins has been promoted, but it is difficult to reuse the colored packages. In particular, PET bottles (bottles formed using PET (polyethylene terephthalate) as a fundamental resin) are required to be colorless at a time when they are treated as recycled materials.
Therefore, in the case of the PET bottles colored with colorant constituted of conventional chemical substances, it is difficult to decolor them, which makes their recycle severe. Although this problem is common to the whole plastic packages, it is particularly serious for the PET bottle because of its amount of usage.
As a measure therefor, packages have been decorated by covering the packages with colored labels and, during the reproduction, the packages themselves are separated from the labels and then processed.
This method satisfies recycle properties of the packages themselves, but it is necessary to peel and separate the labels from the packages after their use.
On the other hand, there are cases where coloration is made by not a chemical coloring mechanism but a physical coloring mechanism in which reflection or interference of the light is utilized.
For example, Japanese Patent Laid-Open No. 80928/1996 proposes a package which develops a chromatic color by providing, on an outer layer of a thermoplastic resin layer, a layer containing a scaly thin film having a high refractive index so that the scaly thin film may be oriented in a plane direction of the surface of the package.
In the package, however, a large amount of a mica/titanium pigment or the like is used as the scaly thin film, and hence, separation of the material is necessary during the recycle, which still makes their recycle severe. Therefore, the above method of the coloration by the physical coloring mechanism is not allowed in a flow of the present recycle, as in the case of the above method by the chemical coloring mechanism.
As another example, Japanese Patent Laid-Open No. 250741/1998 (pages 1 to 4, FIGS. 1 to 10) proposes a transparent container in which a laminate film of a predetermined shape having a thin-film interference function is arranged along the inside of a main body of the transparent container.
However, since the transparent container must involve the laminate film therein, this technology is limited to bottles having a mouth part of an inside diameter smaller than that of the body part. Therefore, it is impossible to apply the technology to cups, trays, and the like molded from plastics. In addition, since the laminate film is in contact with contents, there arises a hygienic problem in a case where the contents are foods.
As described above, in the present packages employing the chemical coloring mechanism, the pigments or dyes blended in the packages cannot be removed in the process of the recycle.
Therefore, there is a problem that the packages once colored cannot be remanufactured in the form of the transparent packages.
A flow from the manufacture to the recycle of the packages, e.g., the PET bottles can be mainly classified into a manufacture process, a distribution process, and a collection/remanufacture process, as shown in FIG. 10.
Namely, the PET bottles manufactured by blow molding injection-molded preforms to stretch and orientate them are filled with contents, sold (consumed), and then collected. The collected PET bottles are separated from colored bottles, crushed, washed to separate impurities therefrom, and then reproduced in the form of flakes or pellets.
In such a flow of the manufacture and the recycle, the injection molding and blow molding are conducted in the manufacture process, and melt extrusion is conducted in a re-pelletization step in a collection/remanufacture process. In these steps, stimulations of a high temperature, a high pressure and the like are applied to the material.
However, even when passed through the steps in which such stimulations are applied, the pigments or dyes still remain without the disappearance of colors because of their high coloration stability. Namely, the pigments or dyes permanently maintain the coloration once they are mixed with the PET.
Therefore, there arises a problem that the colored PET bottles cannot be used as starting materials for the PET bottles to be re-manufactured.
In view of such present situations, in Japan and in a field of manufacture/recycle of the PET bottles, the manufacture and distribution of the PET bottles which cannot be reused are restrained. In other words, the coloration of the PET bottles is prohibited in principle from the viewpoints of the improvement of a reuse ratio of the PET bottles and the promotion of the recycle.
In Japan, it is mentioned as one item of material evaluation standards which are self-organized standards that the PET bottles should be colorless and transparent.
The material evaluation standards are guideposts established to evaluate whether or not the PET bottles once manufactured are suitable for the reuse and remanufacture, and they are self-organized agreements in the field of the manufacture/recycle of the PET bottles.
FIG. 11 shows a flow of a reuse suitability test (reuse suitability evaluation) of the PET bottles performed in accordance with the material evaluation standards.
As shown in the drawing, the reuse suitability evaluation is performed for each of reproduced flakes obtained by crushing trial bottles to be evaluated, reproduced pellets obtained by melt molding the reproduced flakes, injection molded plates obtained by injection molding the reproduced pellets, and fibers, bottles and sheets obtained by molding the reproduced pellets.
As evaluation items, there are mentioned “appearance, crush suitability” for the reproduced flakes, “IV, color tone, dry suitability” for the reproduced pellets, “appearance, haze, thermal properties” for the injection molded plates, and “moldability, mechanical properties, color tone, haze, etc.” for the fibers, the bottles and the sheets.
Particularly, among these evaluation items, “the color tone” is the evaluation item which is investigated in a wide range including the reproduced pellets, fibers, bottles and sheets.
If the trial bottles are contaminated with a pigment or a dye, they remain colored with the pigment or the like even at a stage where they are molded into the reproduced pellets, and hence, they do not satisfy the evaluation standards of “the color tone”. In addition, the color of the trial bottles still remains even at a stage where they are molded into the fibers, the bottles or the sheets, and therefore, the evaluation standards of “the color tone” are not satisfied herein, either.
As described above, the PET bottles mixed with the pigment or the dye do not satisfy the material evaluation standards, and for this reason, they cannot be used as starting materials for the reproduction. Therefore, the coloring of the PET bottles is voluntarily restrained in makers of the PET bottles.
As understood from the above, it is essential from the viewpoint of recycle promotion to evaluate the suitability of the PET bottles to be reused in accordance with the reuse suitability evaluation based on the material evaluation standards. On the other hand, it is also necessary that “the color tone” is evaluated in the suitability test to reject the colored PET bottles.
As mentioned above, however, the coloring of the containers molded as the PET bottles for the purpose of providing functions such as a visible light barrier and a decoration has been desirable from various viewpoints of preventing the change in quality and deterioration of contents therein, promoting the commercialization of new products, differentiating them from other products, promoting the sales of own products, and the like.
In view of such situations, in the field of the manufacture/recycle of the PET bottles, it has been required to propose a technology of providing consumers with the PET bottles which conform to the evaluation items of the reuse suitability evaluation and simultaneously have functions such as the visible light barrier and the decoration. In other words, there has been desired a technology which is capable of providing the colored PET bottles in a distribution process and simultaneously capable of decoloring the PET bottles in a collection/remanufacture process.
The present invention has been developed in consideration of the above circumstances, and an object of the present invention is to provide a plastic package and a method for its reproduction which permits possessing functions such as the visible light barrier and the decoration in the distribution process, satisfying the evaluation standards of the reuse suitability evaluation in the collection/remanufacture process, and improving of a reuse ratio of the packages s to promote the recycle of them.